ATO - Cheap, safe, well explained(?)

[mooker]

Hi all,

 

The following is originally from my IM Fusion 10 thread -- HarryPotter told me to give this it's own post, so here it is!

 

V1 of the DIY ATO is installed and working!

 

I'm going to include a medium-detailed writeup, in case someone needs to use it as reference. This is all synthesized from various sources around the internet, but I figured it'd be nice to have it all in one place.

 

First, the circuit schematic:

 

 

Basic Idea: When the water level falls, it closes Float Switch 1 which sends voltage across the relay. That closes the relay, allowing power to reach the pump, filling your tank with water. When the water level rises again, the switch opens and the power to the pump is cut.

 

Check the bottom of this post for a more detailed explanation about switches and states, including how the failsafe works.

 

Float Switches: I use two float switches for redundancy, one placed at a higher level than the other. They could both be at the same level, it doesn't really matter. The switches are wired in series, so if just one of them is open, the pump won't turn on. I sourced the float switches from amazon at about $4/switch.

 

The Relay: The relay is used to control power delivery to the the pump. I can't just use a switch, as the pump will draw (significantly) more current than the switches are rated for, which is very dangerous. https://en.wikipedia.org/wiki/Relay#Basic_design_and_operation is a good place to find more information about how relays work. I used a 12V automotive relay, a little under $5 on amazon.

 

The Pump: I chose a 12V brushless DC submersible pump to lift the water into my tank. Brushless pumps tend to last longer and be quieter than other options. $9 on amazon.

 

Power Source: I used a standard 12V power supply. There are a lot of options, I chose one that included an adapter to connect it to the rest of my circuit, which ended up being very useful. $7 on amazon.

 

Below is the whole circuit connected and set up for testing:

 

I glued the pump into the bottom of a large (3 gal) BPA-free Tupperware container (by far the most expensive part of this ATO, at $20). The bright pink things you see the float switches attached to are 3D printed brackets I made to attach them to my tank.

Here's a shot of the ATO reservoir under my tank:

And a shot of the float switches:

More detailed explanation of how this works:

The "normal" state of the system is (with float switch 1 being the primary and float switch 2 being the backup):

Water Level: Nominal, the water level I want my tank to be.

Float Switch 1: Open, because the nominal water level raises the float to open the switch.

Float Switch 2: Closed, because the nominal water level is not high enough to open it, it is set to open when water reaches critical levels

Pump: Off

The "top off needed" state of the system is:

Water Level: Below nominal, due to evaporation.

Float Switch 1: Closed, because water level has fallen below nominal

Float Switch 2: Closed because the water level is even lower than "normal" system state

Pump: On

Once the pump turns on in the "top off needed" state, the water level rises until it is high enough to open Float Switch 1 and return the tank to the "normal" state.

However, if for whatever reason the water doesn't open Float Switch 1 at the nominal level, then the pump stays on and the system enters the "Overflow" state.

"Overflow" system state:

Water Level: Above nominal

Float Switch 1: Closed, because it is stuck closed even though water level is above nominal

Float Switch 2: Closed because the water level has not yet reached critical levels

Pump: On

In the "Overflow" system state, the pump stays on and the water level continues to rise even though the water level is above nominal. This is because Float Switch 1 is somehow stuck closed. The water level is not yet critical. As the water level reaches dangerous levels, the system enters the "Failsafe" state.

"Failsafe" state:

Water Level: Critical

Float Switch 1: Closed, because it is stuck closed even though water level is above nominal

Float Switch 2: Open, because the water level has reached critical levels, where this switch is set to open.

Pump: Off

For water to actually overflow out of the system, both Float Switch 1 and Float Switch 2 should have to get stuck closed.

It's working great so far, but I don't trust it enough to just leave it plugged in yet. I'm going to put as much of the wiring and components into a tupperware as I can, and I'll put a RC outlet between it and the wall so I can control it with my rPI.

Let me know if you have any questions!

[Rural]

how would you incorporate another failsafe for the main triggered float switch if it fails. (like have another float lower and is a fail safe if the higher one sticks?) that was always my problem. not overflow, but not triggering on.

[mooker]

how would you incorporate another failsafe for the main triggered float switch if it fails. (like have another float lower and is a fail safe if the higher one sticks?) that was always my problem. not overflow, but not triggering on.

 

Good question! What you'd do is wire that lower float switch in parallel with the nominal water level float switch:

 

 

Then, when the nominal switch sticks open, the tank should behave like this:

 

[mooker]

I spent last night re-wiring the ATO to make it a little cleaner looking and a little more robust.

 

First, I soldered and added heatshrink to all the connections. Then I moved as much wiring as I could into a tupperware container:

 

 

During this process, I decided to add a JST-XH 4 pin connector so that I could unplug the power supply/relay from the rest of the system. I also added some stylish purple braided sleeving to neaten up the wires coming from the float switches

 

 

Here's what the system looks like in situ:

 

 

Closeup of improved cabled situation:

 

[pewpewkittah]

Amazing write up! I think I am gonna have to try to put mine together again. I picked up the wrong kind of relay before and never could get it working.

[mooker]

Amazing write up! I think I am gonna have to try to put mine together again. I picked up the wrong kind of relay before and never could get it working.

 

Thanks! The relay I used was this one: http://smile.amazon.com/Absolute-RLS125-12-VCD-Automotive-Relay/dp/B0002KR9GG?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o04_s00

 

And the power supply I used was this one: http://smile.amazon.com/RockBirds-12V-Switching-Supply-Adapter/dp/B00VM292AO?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s00

[Oracus]

Do you have the STL's for the brackets?

[Jellyingabout]

How has this held up over time? Has salt creep been an issue for the electricals?

[JBM]

22 hours ago, Jellyingabout said:

How has this held up over time? Has salt creep been an issue for the electricals?

 

salt creep is always an issue when it comes to any electrical device in our tanks. That should be on your weekly list of things that you need to rinse with fresh water or clean.

 

Also be in mind, that most cheap float switches will not handle more than 1 amp. (read most amazon float switches)

[Jellyingabout]

20 minutes ago, JBM said:

salt creep is always an issue when it comes to any electrical device in our tanks. That should be on your weekly list of things that you need to rinse with fresh water or clean.

True, but eventually corrosion will win anyway. I'm asking if salt creep has corroded the electrical on this too far considering they're not sealed in the same way many commercial ATOs are built.

[JBM]

If the bulk of the electronics are kept away from the tank. Which in this case they are, and in a sealed Tupperware they should last indefinitely. The float switches are considered consumable/ replaceables. 

[Jellyingabout]

16 minutes ago, JBM said:

The float switches are considered consumable/ replaceables. 

how often do they end up needing rewired/replaced?

[HarryPotter]

On 4/15/2018 at 6:40 PM, Jellyingabout said:

How has this held up over time? Has salt creep been an issue for the electricals?

 

I saw it this weekend in person. Still going strong with no issues!

[HarryPotter]

58 minutes ago, Jellyingabout said:

how often do they end up needing rewired/replaced?

 

Been two years and he still has originals. They don’t need to be rewired or replaced unless you manage to break them- super simple tech.

[JBM]

That's good to know

[Jellyingabout]

21 hours ago, HarryPotter said:

 

I saw it this weekend in person. Still going strong with no issues!

Sold! i'll be trying this out myself

[HarryPotter]

2 minutes ago, Jellyingabout said:

Sold! i'll be trying this out myself

 

You have a printer?

[Jellyingabout]

1 minute ago, HarryPotter said:

You have a printer?

No printer but i work with a lot of acrylic from my Jellyfish tank making days. I'm fairly certain i can put something together similar. I found the float valves and relay etc on ebay all for less than £4 ($5.7)